1. Field of the Invention
The present invention relates to an object separating apparatus and method, and a method of manufacturing a semiconductor substrate.
2. Description of the Related Art
A substrate (SOI substrate) having an SOI (Silicon On Insulator) structure is known as a substrate having a single-crystal Si layer on an insulating layer. A device using this SOI substrate has many advantages that cannot be achieved by ordinary Si substrates. Examples of the advantages are as follows.
(1) The integration degree can be increased because dielectric isolation is easy.
(2) The radiation resistance can be increased.
(3) The operating speed of the device can be increased because the stray capacicance is small.
(4) No well step is necessary.
(5) Latch-up can be prevented.
(6) A completely depleted field-effect transistor can be formed by thin film formation.
Since an SOI structure has the above various advantages, researches have been made on its formation method for several decades.
As one SOI technology, an SOS (Silicon On Sapphire) technology by which Si is heteroepitaxially grown on a single-crystal sapphire substrate by CVD (Chemical Vapor Deposition) has been known for a long time. This SOS technology was once recognized as the most matured SOI technology. However, the SOS technology has not been put into practical use to date because, e.g., a large amount of crystal defects are produced by lattice mismatch in the interface between the Si layer and the underlying sapphire substrate, aluminum that forms the sapphire substrate mixes in the Si layer, the substrate is expensive, and it is difficult to obtain a large area.
Various SOI technology appeared following the SOS technology. For these SOI technologies, various methods have been examined aiming at reducing crystal defects or manufacturing cost. There are a method of implanting oxygen ions into a substrate to form a buried oxide layer, a method of bonding two wafers via an oxide film and polishing or etching one of the wafers to leave a thin single-crystal Si layer on the oxide film, and a method of implanting hydrogen ions to a predetermined depth from the surface of an Si substrate having an oxide film, bonding the Si substrate to the other substrate, and peeling the latter substrate (the other substrate) by a heat treatment while leaving a thin single-crystal Si layer on the oxide film.
The present applicant has disclosed a new SOI technology in Japanese Patent Laid-Open No. 5-21338. In this technology, a first substrate obtained by forming a non-porous single-crystal layer on a single-crystal semiconductor substrate having a porous layer is bonded to a second substrate via an insulating layer (SiO2), and the two substrates are separated from the porous layer to transfer the non-porous single-crystal layer to the second substrate. This technology is advantageous in that the SOI layer has high film thickness uniformity, the crystal defect density in the SOI layer can be decreased, the SOI layer has high surface planarity, no expensive special fabrication apparatus is necessary, and SOI substrates having SOI films about a few hundred xc3x85 to 10 xcexcm thick can be fabricated by the same fabrication apparatus.
In addition, the present applicant has disclosed another technology in Japanese Patent Laid-Open No. 7-302889 in which, after the first and second substrates described above are bonded, the first substrate is separated from the second substrate without breaking, and the separated first substrate is reused by smoothening the surface and again forming a porous layer. Since the first substrate can be economically used, this technology has the advantages that the fabrication cost can be largely reduced and the fabrication process is also simple.
In the above technologies, however, when the two bonded substrates are separated it is necessary to prevent damages to the substrates and protect the fabrication apparatus and the like from contamination caused by the generation of particles.
The present invention has been made in consideration of the above situation, and has as its object to apply a separating apparatus and method suitable to separate semiconductor substrates or other objects, and a method of manufacturing a semiconductor substrate.
According to the present invention, there is provided a separating apparatus characterized by comprising jet means having a fluid jet unit for ejecting a jet of fluid to an object to be separated to separate the object, and control means for changing a condition for ejecting the fluid from the jet unit in accordance with progress of object separation processing.
The separating apparatus preferably further comprises a holding portion for holding the object to be separated.
In the separating apparatus, preferably, the object to be separated has a plate shape, and the holding portion holds the plate-like object to inject the fluid against the plate-like object in a planar direction thereof.
In the separating apparatus, the control means preferably changes a pressure of the fluid to be ejected from the jet unit in accordance with progress of object separation processing.
In the separating apparatus, the control means preferably controls the jet means to set the pressure of the fluid to be relatively high in separating a vicinity of a peripheral portion of a separation surface of the object to be separated.
In the separating apparatus, the control means preferably controls the jet means to set the pressure of the fluid to be relatively high in separating a vicinity of a central portion of a separation surface of the object to be separated.
In the separating apparatus, the control means preferably controls the jet means to set the pressure of the fluid to be relatively high in separating vicinities of peripheral and central portions of a separation surface of the object to be separated and controls the jet means to set the pressure of the fluid to be relatively low in separating an intermediate portion between the vicinities of the peripheral and the central portions.
In the separating apparatus, the control means preferably changes the condition for ejecting the fluid from the jet unit in accordance with a relative positional relationship between the jet unit and the object to be separated.
In the separating apparatus, the control means preferably changes the condition for ejecting the fluid from the jet unit as a function of time.
The separating apparatus preferably further comprises scanning means for scanning the jet unit.
The separating apparatus preferably further comprises rotating means for rotating the object about an axis perpendicular to a separation surface of the object to be separated.
The object to be separated preferably has a fragile layer as a separation layer. The fragile layer is preferably a porous layer or a layer having a microcavity.
According to the present invention, there is provided a separating method of separating an object by ejecting a jet of fluid from a jet unit to the object to be separated, characterized by comprising the control step of changing a condition for ejecting the fluid from the jet unit in accordance with progress of object separation processing.
In the separating method, preferably, the object to be separated has a plate shape and is separated by injecting the fluid against the plate-like object in a planar direction thereof.
In the separating method, the control step preferably comprises changing a pressure of the fluid to be ejected from the jet unit in accordance with progress of object separation processing.
In the separating method, the control step preferably comprises setting the pressure of the fluid to be ejected from the jet unit to be relatively high in separating a vicinity of a peripheral portion of a separation surface of the object to be separated.
In the separating method, the control step preferably comprises setting the pressure of the fluid to be ejected from the jet unit to be relatively high in separating a vicinity of a central portion of a separation surface of the object to be separated.
In the separating method, the control step preferably comprises setting the pressure of the fluid to be ejected from the jet unit to be relatively high in separating vicinities of peripheral and central portions of a separation surface of the object to be separated and setting the pressure of the fluid to be ejected from the jet unit to be relatively low in separating an intermediate portion between the vicinities of the peripheral and the central portions.
In the separating method, the control step preferably comprises changing the condition for ejecting the fluid from the jet unit in accordance with a relative positional relationship between the jet unit and the object to be separated.
In the separating method, the control step preferably comprises changing the condition for ejecting the fluid from the jet unit as a function of time.
The separating method preferably further comprises executing separation processing for the object while scanning the jet unit along the separation surface of the object to be separated.
The separating method preferably further comprises executing separation processing for the object while rotating the object about an axis perpendicular to the separation surface of the object to be separated.
In the separating method, the object to be separated preferably has a fragile layer as a separation layer. The fragile layer is preferably a porous layer or a layer having a microcavity.
According to an aspect of the present invention, there is provided method of manufacturing a semiconductor substrate, characterized by comprising the steps of forming a first substrate in which a porous layer and a non-porous layer are sequentially formed on one surface, bonding the first substrate to a second substrate via the non-porous layer to form a bonded substrate stack, and separating the bonded substrate stack into two substrates while ejecting a jet of fluid to the porous layer of the bonded substrate stack, wherein the separation step comprises changing a condition for ejecting the fluid in accordance with progress of the separation step.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor substrate, characterized by comprising the steps of implanting ions from a surface of a substrate consisting of a single-crystal semiconductor to a predetermined depth, thereby forming a first substrate in which a microcavity layer is formed, bonding a second substrate to a front surface side of the first substrate to form a bonded substrate stack, and separating the bonded substrate stack into two substrates while ejecting a jet of fluid to the microcavity layer of the bonded substrate stack, wherein the separation step comprises changing a condition for ejecting the fluid in accordance with progress of the separation step.
Further objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.